[GHC] #14963: ghci -fdefer-type-errors can't run IO action from another module

[GHC]

#14963: ghci -fdefer-type-errors can't run IO action from another module
-------------------------------------+-------------------------------------
           Reporter:  elaforge       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.4.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This is enough to trigger a crash on OS X and Linux:

 Bug1.hs:
 {{{
 module Bug1.hs where
 import qualified Bug2

 test :: IO Bool
 test = Bug2.failure
 }}}

 Bug2.hs:
 {{{
 module Bug2 where

 failure :: IO Bool
 failure = return False
 }}}

 Shell:
 {{{
 % ghci -fdefer-type-errors -ignore-dot-ghci
 GHCi, version 8.4.1: http://www.haskell.org/ghc/  :? for help
 Prelude> :load Bug
 [1 of 2] Compiling Bug2             ( Bug2.hs, interpreted )
 [2 of 2] Compiling Bug              ( Bug.hs, interpreted )
 Ok, two modules loaded.
 *Bug> test
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.4.1 for x86_64-apple-darwin):
         nameModule
   system $dShow_a1LX
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in
 ghc:Outputable
         pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 This is specific to 8.4.1, in 8.0.2 I get "False" as expected.  If I leave
 off -fdefer-type-errors, it works.  It also seems to be ghci only,
 compiling with -fdefer-type-errors doesn't have the problem.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14963>
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